Researchers from the National Institute for Materials Science in Japan have developed new additives for the hole-transporting layer of perovskite solar cells, which aim to greatly improve cell stability. When placed in the dark, the cells did not show signs of deterioration even after 1,000 hours of testing, and under continuous light soaking, they lasted six times longer (in terms of the time it takes for their power conversion efficiencies to fall to 85% of their initial states) compared to cells treated with conventional additives.

The researchers hope that these results will accelerate the commercialization of perovskite solar cells. The research group directed its focus on a pyridine-based additive, TBP, which is used as an additive in a hole-transporting layer in the mesoporous-type cell structure. After conducting experiments and analyzing the results, the group found that chemical reactions occurring between TBP and perovskite materials were one of the major causes of stability deterioration.

Analyses using infrared spectroscopy and X-ray diffraction revealed that the chemical reaction mainly occurs between the nitrogen atom in the pyridine ring and perovskite crystals. The group successfully suppressed this undesirable reaction and consequently, perovskite solar cells that contained the new pyridine derivatives maintained their performance over 1,000 hours in the dark. In addition, under continuous light exposure, application of conventional additives made cells last for slightly less than 25 hours, which is the time it took for the cells’ conversion efficiencies to decrease to 85% of their initial states. In contrast, application of the new additives made the cells last for 150 hours. That is, the cells’ stability was increased by six times.